Method of etching ferroelectric devices

Abstract

A method of etching a ferroelectric device 100 having a ferroelectric layer 112 between a top and a bottom electrode 114, 108 is disclosed herein. Hardmasks 116, 118 are deposited on the top electrode 114 , two or more hardmasks being spaced apart by narrow first regions 115 and spaced apart from other hardmasks by wider second regions 117 . The top electrode 114 and ferroelectric layer 112 are then etched to pattern the top electrode 114 thus forming capacitors 102, 104 , and the bottom electrode 108 is etched by a process in which the second regions are etched more slowly than the second regions. Those capacitors having a first region between them have a common bottom electrode 108 , but in the second regions the bottom electrode is severed. To pattern the bottom electrode 108 , a fluorine-based chemistry followed thereafter by a CO-based chemistry are used in a two step etching process.

1. A method of etching a ferroelectric device having a ferroelectric layer between a top electrode layer and a bottom electrode layer, the method comprising the steps of:
 depositing a plurality of hardmask elements over the top electrode layer, two or more of said hardmask elements being spaced apart pairwise by first regions and spaced apart from other hardmask elements by second regions, the first regions being narrower than the second regions; 
 etching the device using, during at least the etching of the bottom electrode layer, a two-step etching technique having a first etching step in which the bottom electrode is etched but a protective deposit is formed which protects the bottom electrode in the first regions from further etching, followed by a second step in which the deposits are removed, said technique being more effective in the second regions than the first regions, the bottom electrode layer being completely removed only in the second regions; and 
 forming a protection layer on the hardmask, sidewalls of the top electrode and the ferroelectric layer, and on the bottom electrode, prior to the patterning of the bottom electrode. 
 
     
     
       2. A method according to  claim 1  in which the first etching step comprises etching using a fluorine-based chemistry; and the second step comprises etching the remaining bottom electrode using a CO-based chemistry. 
     
     
       3. A method according to  claim 1  wherein the protection layer is deposited using atomic layer deposition. 
     
     
       4. A method according to  claim 1  wherein the protection layer comprises Al 2  O 3 . 
     
     
       5. A method according to  claim 1 , further comprising the step of anisotropically etching the protection layer so that only the sidewall portions of the top electrode and the ferroelectric layer remain. 
     
     
       6. A method according to  claim 2  further comprising the step of wet cleaning the ferroelectric device after the CO-based chemistry etching.